Poll of the Day > VIDEO: When your camera shutter rate matches helicopter rotor speed!

(+) Yeah! (+)

https://www.youtube.com/watch?v=yr3ngmRuGUc&fbclid=IwAR0I7N146Hu3NukaTtPPrCZR6P9u_9Trqe9zxDfxigvHDvlA_m-Km4PS4vg

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Pretty sure it's just ascending into Heaven.

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So when is Elon going to invent some dank hoverboards for us peasants?

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Turn it into one of those Topic > Board .gifs we used o do a long time ago, or whatever they were.

pretty sure it's more related to compression and/or image stabilizing. I saw a similar effect watching a bicycle video where the front tire appeared to almost be motionless except for turning forward an inch or two once every few seconds. the speed of the tire should be fluctuating a lot, so it's not synchronized with the camera. the compression on the video is just reducing something that is otherwise super hard to compress due to the amount of noise involved into something extremely easy to compress since it's no longer moving frame to frame.

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Similar to the flashing LED lights scenario. I recall seeing a video for a Corvette (years ago), when LED was becoming THE thing. I'm like, wtf, that's embarrassing to show on your Youtube channel- a video of your car's tail light flickering like crazy. It's not a malfunction or faulty connection. They do actually flicker, but too fast for the naked eye.

However, the camera sees all!

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great magneto broke out of his cell again

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Bump

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Sahuagin posted...

pretty sure it's more related to compression and/or image stabilizing. I saw a similar effect watching a bicycle video where the front tire appeared to almost be motionless except for turning forward an inch or two once every few seconds. the speed of the tire should be fluctuating a lot, so it's not synchronized with the camera. the compression on the video is just reducing something that is otherwise super hard to compress due to the amount of noise involved into something extremely easy to compress since it's no longer moving frame to frame.

Compression wouldn't cause this at all. It's totally the video frame rate matching a specific rate of rotation of the object. A wheel with thirty-two spokes would be a lot easier to capture stroboscopic footage of than a helicopter with five propeller blades. You just need the frame rate to match a multiple of 1/32 the rotational speed of the wheel compared to a multiple of 1/5 the helicopter blades. There are many more opportunities to match the wheel compared to the helicopter. Even if you don't match the rotational speed, the video can still appear to show a very slowly moving rotating object if you get close to the ideal amount. The the wheel wasn't completely stationary as it progressed a couple inches every few seconds, so they weren't entirely synchronized to one of those multiples of the wheel.

Here's a related video on the stroboscopic effect:
https://www.youtube.com/watch?v=2SgG99QKLFE

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Energy Surge posted...

Compression wouldn't cause this at all. It's totally the video frame rate matching a specific rate of rotation of the object. A wheel with thirty-two spokes would be a lot easier to capture stroboscopic footage of than a helicopter with five propeller blades. You just need the frame rate to match a multiple of 1/32 the rotational speed of the wheel compared to a multiple of 1/5 the helicopter blades. There are many more opportunities to match the wheel compared to the helicopter. Even if you don't match the rotational speed, the video can still appear to show a very slowly moving rotating object if you get close to the ideal amount. The the wheel wasn't completely stationary as it progressed a couple inches every few seconds, so they weren't entirely synchronized to one of those multiples of the wheel.

Here's a related video on the stroboscopic effect:
https://www.youtube.com/watch?v=2SgG99QKLFE

I was looking for that video after seeing this thread, but I couldn't remember who had done it.

The holographic projector on that scout disk is malfunctioning. Looks like we're picking up some of their bad habits.

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"It is my time, I am needed."

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Energy Surge posted...

Compression wouldn't cause this at all. <snip>

why not? that's exactly the kind of thing compression does to simplify the image to compress it.

here's an example. things to notice include:

• the edges of the back wheel of the other bike are almost but not quite stationary, while the middle of the wheel is very clearly in motion. this is because the pattern on the edge repeats, and the compression is turning something that's "pretty close" to something that's exact. the middle of the tire is messy enough that the pattern doesn't repeat frame to frame, so the compression ignores it.
• even better, at times the rubber on the top of his front tire appears completely motionless. this isn't (just) because it's in synch with the camera, it's because the image on each frame look "pretty close" to the compression, so it converts it into something that's exact frame to frame.

https://www.youtube.com/watch?v=GBUJtUKk5KA&t=25m22s

for the helicopter, you're not literally getting raw frames that look identical frame to frame, you're getting frames that look similar frame to frame and the compression converts it into something that looks identical.

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I don't really know shit about cameras, but why does everything else seem to move, at least somewhat, normally? Shouldn't it look slowed down or kinda choppy like claymation?

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Saying the blades are moving at the same rate as the camera frames are just government lies to cover up this helicopter being abducted by aliens.
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Sahuagin posted...

pretty sure it's more related to compression and/or image stabilizing. I saw a similar effect watching a bicycle video where the front tire appeared to almost be motionless except for turning forward an inch or two once every few seconds. the speed of the tire should be fluctuating a lot, so it's not synchronized with the camera. the compression on the video is just reducing something that is otherwise super hard to compress due to the amount of noise involved into something extremely easy to compress since it's no longer moving frame to frame.

nah. its magic

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Muscles posted...

I don't really know shit about cameras, but why does everything else seem to move, at least somewhat, normally? Shouldn't it look slowed down or kinda choppy like claymation?

This happens because the rotational frequency of the helicopter blades happens to line up with the framerate of the camera. The framerate isn't anything unusually high or low, and presuming the footage is played back at the same rate as it was recorded, there's no reason to expect anything else to look weird.

https://youtu.be/mPHsRcI5LLQ
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Sahuagin posted...

why not? that's exactly the kind of thing compression does to simplify the image to compress it.

here's an example. things to notice include:
* the edges of the back wheel of the other bike are almost but not quite stationary, while the middle of the wheel is very clearly in motion. this is because the pattern on the edge repeats, and the compression is turning something that's "pretty close" to something that's exact. the middle of the tire is messy enough that the pattern doesn't repeat frame to frame, so the compression ignores it.
* even better, at times the rubber on the top of his front tire appears completely motionless. this isn't (just) because it's in synch with the camera, it's because the image on each frame look "pretty close" to the compression, so it converts it into something that's exact frame to frame.
https://www.youtube.com/watch?v=GBUJtUKk5KA&t=25m22s

I might agree compression is involved in causing this effect with the tire tread. When you described a bike wheel, I was imagining a stationary observer watching the bike roll past. The stroboscopic effect is also known as the wagon wheel effect as the spokes of a wagon wheel can do the same thing as propeller blades. I didn't imagine a scenario where the camera is looking at the tire treads which are held relatively stationary in a small part of the frame because the camera is traveling with the tire.

Sahuagin posted...

it can't be for the bicycle wheels though since they're not moving fast enough.

The speed of the wheels doesn't need to be as fast as you think. Yes, an object could turn 360 degrees in one frame to create the effect. That video appears to be 25 fps, so that would require 1500 rpm for the wheel. I agree that's way too fast. But you pointed out the edge of the tread appeared motionless while the center of the tread didn't. For mountain bike tires, the edge of the tread is often lined with a repeating pattern of studs that repeats much more frequently than the studs along the center of the tread.

Let's say there are fifty studs in the tread aloud the edge of the tire just to make the math simple. Because there are fifty identical positions, it could rotate as little as 7.2 degrees per frame to match the frame rate of the camera. That's only 30 rpm. And the wheel could turn any multiple of 7.2 degrees to reach another identical position. So any multiple of 30 rpm would make the studs on the tread appear motionless. 150 rpm is around 10-12 mph depending on the diameter of the tire.

The studs along center don't repeat at the same rate so the effect doesn't manifest down the center of the tread. When they reach the top of the incline they're able to move more quickly and the rate of revolution is able to match one of the speeds capable of causing the center of the tire edge to repeat each frame.

So I think I'll still argue this effect is present in your linked video, though I'm not completely sure.

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Energy Surge posted...

Let's say there are fifty studs in the tread aloud the edge of the tire just to make the math simple. Because there are fifty identical positions, it could rotate as little as 7.2 degrees per frame to match the frame rate of the camera. That's only 30 rpm. And the wheel could turn any multiple of 7.2 degrees to reach another identical position. So any multiple of 30 rpm would make the studs on the tread appear motionless. 150 rpm is around 10-12 mph depending on the diameter of the tire.

yeah k. I think I'm underestimating the speed of a camera shutter, and the visual similarity of the wheel from frame to frame. compression might be involved but now I have no idea to what degree if any.

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